This invention relates to a process for reducing the level of pollutants from the exhaust of a diesel engine. More particularly, this invention relates to a process for reducing the level of pollutants such as NOx and diesel particulate emissions from the exhaust of a diesel engine wherein a water-diesel fuel emulsion is used as the fuel in combination with exhaust after treatment products to treat the engine exhaust.
The term xe2x80x9cNOxxe2x80x9d is used herein to refer to any of the nitrogen oxides NO, NO2, N2O, or combinations thereof. Over the past ten years, increasingly more stringent heavy duty on-highway engine emission regulations have led to the development of engines in which NOx and diesel particulate emissions have been reduced by as much as 70% and 90%, respectively.
The term xe2x80x9cfilterxe2x80x9d used herein refers to any of the after-treatment filters, traps, particulate filters, particulate traps, and the like.
Proposed regulations for new heavy duty engines require additional NOx and diesel particulate emission reductions of over 70% from existing emission limits. These emission reductions represent a continuing challenge to engine design due to the NOx-diesel particulate emission and fuel economy tradeoffs associated with most emission reduction strategies. Emission reductions are also desired for the on and off-highway in-use fleets. Within the heavy duty engine population, it is becoming more apparent that older engines are contributing a disproportionate amount of emissions. Many of these engines have useful lives of over 15 years. To meet the air quality objectives in many regional areas, reductions in NOx and diesel particulate emissions will need to be derived from the in-use, mobile source engine population. In some regional areas, the proposed emission reductions from the engines in-use potentially represent an even greater challenge than the emission limits proposed for new engines.
It is recognized that the engine, lubricants, fuel, and exhaust after-treatments need to be integrated into a system to maximize the control of and reduction of emissions.
Recent engine work focuses on improvements or incorporation of new technologies to the power cylinder, air delivery, fuel management, and electronic systems. These improvements typically satisfy the emission requirements of new engines. Some improvements can also be implemented during the engine rebuild process; however, internal engine modifications are not broadly and practically applicable to in-use fleets.
Some new engines require the use of diesel exhaust after-treatment products to meet diesel particulate matter limits. This technology can be readily retrofitted with generally no engine modifications required.
In the urban environment, health concerns regarding diesel particulate emissions are resulting in thousands of buses being retrofitted with after-treatment technologies such as particulate filters and oxidation catalyst technologies. In the United States, the implementation of the urban bus rebuild/retrofit requirements increased interest in emission reduction technologies for in-use heavy duty diesel vehicle fleets.
Diesel fuel improvements have been introduced in most parts of the developed world to provide reductions in particulates and NOx from the vehicle fleets in current operation as well as to facilitate the introduction of after-treatment devices. Reducing the sulfur content and the xe2x80x9cheavy endxe2x80x9d of the fuel have been the key changes. In the United Kingdom, the government has offered tax incentives to initiate the use of a grade of diesel fuel termed ultra low sulfur diesel (ULSD), which has a maximum 50 parts per million (ppm) sulfur content and a 95% distillation temperature of less than 345xc2x0 C. As well as achieving immediate reductions in particulates and NOx from the current vehicle fleet, the availability of ULSD was intended to encourage the use of after-treatment technologies of particulate filters, oxidation catalysts and the like.
Diesel fuel improvements typically involve the reduction of fuel sulfur via hydrotreating to levels as low as 10 ppm (Swedish Mk 1 fuel). Other fuel parameters such as aromatics and cetane have also been the subject of investigation. Specially manufactured fuels and the incorporation of special fuel components such as biodiesels, Fisher Tropsch blends, methanol, and ethanol, are also gaining attention.
While many of the foregoing suggestions are meritorious, the problem remains that further reductions in pollutants, especially NOx and diesel particulate emissions, are required. The inventive process provides a solution to this problem.
This invention relates to a process for reducing the level of pollutants in the exhaust of a diesel engine, comprising: operating said diesel engine using as the fuel a water-diesel fuel emulsion; and contacting the exhaust from said diesel engine with a particulate filter/trap.
The water-diesel fuel emulsion is comprised of water, diesel fuel and an emulsifier. The emulsifier comprises: (i) at least one fuel-soluble product made by reacting at least one hydrocarbyl-substituted carboxylic acid acylating agent with ammonia or an amine, the hydrocarbyl substituent of said acylating agent having about 50 to about 500 carbon atoms; (ii) at least one of an ionic or a nonionic compound having a hydrophilic-lipophilic balance (HLB) of about 1 to about 40; (iii) a mixture of (i), (ii); (iv) a water-soluble compound selected from the group consisting of amine salts, ammonium salts, azide compounds, nitrate esters, nitramine, nitro compounds, alkali metal salts, alkaline earth metal salts, in combination with (i), (ii) or (iii); (v) the reaction product of polyacidic polymer with at least one fuel soluble product made by reacting at least one hydrocarbyl-substituted carboxylic acid acylating agent with ammonia, an amine or a polyamine and (vi), a mixture of (ii) and (v).
The process for making an aqueous hydrocarbon fuel composition comprises:
a) mixing a liquid hydrocarbon fuel and at least one emulsifier to form a hydrocarbon fuel emulsifier mixture; and
b) mixing the hydrocarbon fuel emulsifier mixture with water or water and ammonium nitrate under emulsification conditions to form an aqueous hydrocarbon fuel composition, wherein the aqueous hydrocarbon fuel composition includes a discontinuous phase, the discontinuous aqueous phase being comprised of aqueous droplets having a mean diameter of 1.0 micron or less.
The filter system generally contains the following components: filter medium, regeneration system and monitoring system. The filter reduces the particulate matter emissions that are generally created during combustion and normally emitted with the exhaust.
It has been found that by using the combination of a water-diesel fuel emulsion and a diesel particulate filter to treat the exhaust from the engine that improvements occur in exhaust emissions of PM (particulate matter) and NOx.
In regards to diesel particular filters (DPF""s), there are two key characteristics of the combustion of water-blended fuel. First, the use of water-blended fuel reduces the diesel particulate matter emissions emitted by the engine. Second, the reduction in the diesel particulate matter emissions is largely a reduction of the insoluble carbon portion. The reduction of the insoluble carbon portion of the emitted diesel particulate results in a higher proportion of the volatile organic portion.
The following improvements are apparent:
That an engine running water-blended fuel equipped with a diesel particulate filter displays a lower particulate accumulation rate in the diesel particulate filter and lower back pressure due to the favorable change in soot permeability. This in turn promotes better fuel economy or the capability to reduce the size of the diesel particulate filter.
That the lower accumulated diesel particulate matter mass in a diesel particulate filter is characterized by a lower proportion of the insoluble carbon portion and a higher proportion of the volatile organic portion. The reduced engine-out particulate mass which is a direct result of combusting an emulsified fuel means that less particulate will be accumulated under low exhaust temperature conditions. This will extend the use of diesel particulate filters to applications with lower exhaust temperatures. Further, the shift to higher proportion of volatile organics will result in additional reductions in exhaust restriction as a result of the increased combined permeability for accumulated soot and diesel particulate filter material.
That an engine running water-blended fuel equipped with a diesel particulate filter which relies on an exhaust fuel burner, electric heater, thermal and non-thermal plasma, microwave, engine control measures (i.e., fuel injection timing, control of turbocharging, and the like) or other external supply of heat to regenerate; that the DPF requires less frequent regeneration and uses less fuel/electrical energy or other energy during regeneration.
That any engine running water blended fuel equipped with a diesel particulate filter that relies on passive regeneration (filter supported heterogeneous soot ignition catalysts or fuel borne soot ignition additive/catalysts) or continuous regeneration (through the generation of nitrogen dioxide (NO2), requires regeneration less often. Thus, the use of water blended fuel and a diesel particulate filter effectively extends the operational low temperature limit of passive or continuous catalyst systems, which allows passive or continuous regeneration strategies to be employed on vehicles with colder vehicle duty cycles.